On Tue, Jun 16, 2020 at 2:53 AM Borislav Petkov <[email protected]> wrote: > > Ok, > > here's the fix first so that it goes in. I'll hammer on the test case later.
Does the 32-bit case need FNINIT? > > --- > From: Petteri Aimonen <[email protected]> > > Previously, kernel floating point code would run with the MXCSR control > register value last set by userland code by the thread that was active > on the CPU core just before kernel call. This could affect calculation > results if rounding mode was changed, or a crash if a FPU/SIMD exception > was unmasked. > > Restore MXCSR to the kernel's default value. > > [ bp: Carve out from a bigger patch by Petteri, add feature check. ] > > Signed-off-by: Petteri Aimonen <[email protected]> > Signed-off-by: Borislav Petkov <[email protected]> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=207979 > --- > arch/x86/include/asm/fpu/internal.h | 5 +++++ > arch/x86/kernel/fpu/core.c | 3 +++ > 2 files changed, 8 insertions(+) > > diff --git a/arch/x86/include/asm/fpu/internal.h > b/arch/x86/include/asm/fpu/internal.h > index 42159f45bf9c..845e7481ab77 100644 > --- a/arch/x86/include/asm/fpu/internal.h > +++ b/arch/x86/include/asm/fpu/internal.h > @@ -623,6 +623,11 @@ static inline void switch_fpu_finish(struct fpu *new_fpu) > * MXCSR and XCR definitions: > */ > > +static inline void ldmxcsr(u32 mxcsr) > +{ > + asm volatile("ldmxcsr %0" :: "m" (mxcsr)); > +} > + > extern unsigned int mxcsr_feature_mask; > > #define XCR_XFEATURE_ENABLED_MASK 0x00000000 > diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c > index 06c818967bb6..f398fedc590a 100644 > --- a/arch/x86/kernel/fpu/core.c > +++ b/arch/x86/kernel/fpu/core.c > @@ -101,6 +101,9 @@ void kernel_fpu_begin(void) > copy_fpregs_to_fpstate(¤t->thread.fpu); > } > __cpu_invalidate_fpregs_state(); > + > + if (boot_cpu_has(X86_FEATURE_XMM)) > + ldmxcsr(MXCSR_DEFAULT); > } > EXPORT_SYMBOL_GPL(kernel_fpu_begin); > > -- > 2.21.0 > > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette -- Andy Lutomirski AMA Capital Management, LLC
